Roentgenometer



Aug. 8, 1939. s. YEDA ROENTGENOMETER Filed Feb. 5, 1957 Patented Augl-S, 1939 ROENTGENOMETER Shuzo Yoda, Tokyo, Japan, asslgnor to Choshlchi Yamagoshi,

Tokyo, Japan Application February 5, 1937, Serial No; 124,191

In Japan October 3, 1936 6 Claims.

This invention relates to dosimeters or roentgenometers for measuring the intensity of a beam of Roentgen rays.

Generally, it is known that, in a chamber, air

is ionized by projecting Roentgen rays thereinto,

the degree of ionization thereby produced depending on the intensity of the rays. Various devices have been proposed to measure the intensity of the Roentgen rays by measuring the said degree of ionization. According to this invention, the intensity of the Roentgen rays is measured by measuring the additional electric potential which is necessary to be supplied to make up the electric potential lost by the neutralization of ions in the chamber due to the projection of X-rays thereinto.

According to this invention, a variable condenser, one pole of which is electrically connected with an electrode arranged in the ionization chamber, is initially charged at a predetermined potential, and then a beam of X-rays is projected for a certain time into the ionization chamber to ionize the air in the chamber. The initial charge set up in the electrode arranged in the chamber, and consequently the initial charge in the pole connected with the said electrode, is.

reduced by the neutralization of ions in the chamber.

Next, by adjusting the variable condenser, the predetermined potential of the initial charge may be restored. The difference between the original position and the adjusted position of the movable pole of the variable condenser or the difference of indication of the "dial of said condenser shows the additional potential employed to restore the initial charge and thus, indirectly, the intensity of the Roentgen rays. The variation of the potential of the condenser is indicated by an electrometer by means of which the potential of the initial charge may be observed and the potential of the restored charge may likewise be observed and caused to coincide therewith.

The principal object of the present invention is in increasing the constancy in operation of such an instrument, enabling accurate measurements to be carried out without periodical calibrations.

Another object of the invention is to provide an instrument by means of which measurements can be carried out for a wide range of intensity of Roentgen rays.

A further object of the invention is to provide an instrument in which stray radiations received by observers during measurements can safely be disregarded.

Other objects and various features of the invention making for economy in manufacture and efficiency in operation will be more apparent from the following description when read in connection with the accompanying drawing, in which,

Figure 1 is an elevational view, partly in section and more diagrammatically illustrated, showing a dosimeter according to the invention.

Figure 2 is a fragmentary cross sectional view of the ionization' chamber of the apparatus shown in Figure 1, section being taken at the line 2-2, Figure 1.

Figure 3 is a view of the fibre of an electrometer as observed through a microscope in association with a scale provided on a rotatable eyepiece of a microscope or other rotatable portion of the latter which is in the line of vision.

Figure 4 is a plan view of the device illustrated in Figure 1, partially broken away.

Referring to the drawing, and more particularly to Figures 1 and 2, l is a metallic casing for enclosing and shielding the main parts of the instrument and is preferably made of lead. 2 is a collecting electrode, preferably discoidal, projecting into an ionization chamber 3 formed within the casing by the rear wall of the casing and a partition wall 4, preferably of ebonite. The electrode 2 is mounted on a metallic rod 5 which is supported by and insulated from the partition wall 4 by means of amber rings 6. On the opposite end of the metallic rod 5 is mounted one pole or plate of the variable condenser l which is composed of a pair of semi-circular plates. The rod 5 is also connected to fibre electrometer 8. The said electrometer, as best seen in Fig. 5, comprises a substantially fixed plate 29 mounted upon and electrically connected to the casing l and a preferably gold covered quartz fiber 30 hanging in substantially parallel relation to said plate 29, but insulated therefrom. The plate 29 may preferably be carried on a threaded rod 29a which extends through the easing I, and the horizontal adjustment of said plate relatively to the fiber 30 may be controlled by an adjusting nut 29b which is threaded upon said rod. The other plate of the variable condenser is mounted on a rod 8 which is extended to the outside of the casing l and rotatably supported by the front wall of the casing. To the outward extremity of the rod 9 is fixed a knob l0 iii provided with a dial or indicator II for regulating the variable condenser.

i2 is a source of direct current, one terminal of which is connected through a push button I! to 2 the I and the othert'ermlnal is connected to the casing. as shown. it is -a microscope' for observing the ilbre oi the electrometer I. The microscope is acommonly used-type which'is angulariy adjustable aboutpivot it by operating a screw device-ll, and also rotatably adjustable,-

at least in part, about its own axis. 1

It is common to provide, in suchmicroscopes.

an eye-piece which has formed thereon or therein, a scale 21. Any pointon this scale, as for example, the zero mark, may be brought into horizontal register with matter being inspected by lateral adjustment of the microscopeby the manipulation of the screw device", and such point may be brought into diagonal register with suchmatter by rotation of the eye-piece about the longitudinal axis of the microscope.

'Ihe. lateral wall of the casing I is iormed, at

the portion adjacent the-ionization chamber 3. with a window it for admitting therethrough a beam of X-rays, the intensity of which is to be I measured. The effective-opening of this window may be regulated by means of an adjustable stop il consistin'g of a rotatabledisc provided with a series of apertures it of diii'erent diameters adapted to be brought at will in alignment with the window It. I! is a shutter rockably pivoted,

as at a. to the stationary part of the device and To measure the intensity of X-rays, the vari,

able condenser I is atilrst set at its full capacity and is charged, together with the collecting electrode 2 and the electrometer l, at a certain known potential by pressing the key l3 thus causing the fibre 26, to be deflected and assume an angular or diagonal position. In this case, the potential at which theinsulated system 2, 5, I and 8 is charged must be suillciently high to cause th saturation current to flow in the ioni- 1 zation chamber 3.

. same angulariy by means of adjustable screw l- Microscope ll is then adjusted by moving the androtating the same or its eyepiece or other rotatable part, with the scale 21, about the longitudinal axis of the microscope in such a manner that the fibre 26 of the electrometer as viewed through the microscope rests at zero position of its scale 21, as shown in Figure 3, whereupon the shutter is is opened for a certain predetermined short length of time for permitting X-rays to enter the ionization chamber 3 through the window I I by way of one of the apertures it provided on the disc il. After the exposure, the

air in the chamber 2 is ionized, so that the electrode 2-is partially discharged and the potential 1 thereof is reduced depending on the intensity oi the x-rays. As a result, the fibre 2 of the electrometer has moved out of alignment with the zero line of the scale 21. The capacity of the variable condenser is then reduced by operating onthe knob It so as to bring the potential of the insulated system back to its initial value of electric potential, as indicated by the return of the fibre to zero position on'the scale 21,

*and the reading is yindicator il.

then taken at the dial or Atv a. fixed condition. there exists a certain linear relationship between the intensity 0! X-rays and the decrease of capacity oi the \ari-.

able condenser. -..'I 'herefore, it is possible to measure indirectlyth'e intensity of x-rays by differences in the readings'taken at the dial ll before the projection of the x-raysinto the ionization chamber and after the restoration of the '-potential of the insulated system by changing a in the case of known dosimeters of this sort.

By the provision of the shutter Is it is made possible to admit X-rays into the: ionization chamber. 2 at a certain constant condition oi! radiation. Moreover,v the observer is protected i'rom stray radiations, as there is no need to observe the movement of fibre under a radiated condition. The adjustable stop consisting of a disc provided with apertures of different sizes serves to control the range of X-ray intensity which can be measured.

What I claim is:

1. Aroentgenometeror the like, comprising a metallic casing including an ionization chamber provided with an opening for admitting X-rays thereinto, an electrode projecting into said chamher and insulated from said casing, an electrometer electrically connected to said electrode, optical means for observing the condition of said electrometer, and a variable condenser one plate of which is electrically connected with said electrode and electrometer and the other plate oi. which is adjustable and hasan indicator connected thereto, permitting observation and comparison of the various settings of said condenser, the latter being a part of an electric circuit which includes said electrode and electrometer and being adapted, by variationv thereof, to provide compensation changes caused therein by the admission of X-rays into the ionization chamber.

2. A roentgenometer or the like, according to claim 1, further characterized in including a source of electric energy connected to and adapted to establish an electric potential in said electrode and electrometer prior to the admission oi! X-rays into the ionization chamber.

3. A roentgenometer or the like, according to claim 1, further characterized in including an adjustable stop disposed adjacent to said opening.and adapted to variably control the breadth of the beam of rays to be admitted into the ionization chamber.

in said circuit for potential 4. A roentgenometer or the like, according to I CERTIFICATE OF CORRECTION. Patent No. 2,l68-,h6h.. 7 August 8, 1959.

SHUZO YEDA,

It is hereby certifiedthat error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, second column, line 20, after the word and period "away." insert the following paragraph 7 I Fig. Sisafragmental vertical sectional view on the line Y 5-5of Fig. 1 illustrating the details of an electrometer which may be employed in the present invention and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 19th day of September, A. D. 1939.-

Henry Van Arsdale, (Seal) Acting Commissioner of Patents, 

